Frequency, pulse length, and the mechanical index

As currently defined, the mechanical index (MI) uses only two parameters, peak rarefactional pressure and center frequency. The effect of another important factor, the pulse length (L-P), was investigated by numerical computations for cavitation threshold (P-t) similar to the analytical work underlying the MI. The effect of LP on P-t is small for the original threshold criterion (maximum temperature, T-max=5000 K), but can be substantial for the often-used criterion on maximum radius, R-max=2R(0). The potential for bioeffects produced by purely mechanical means (R-max) increases with LP, while those mediated by sonochemicals (T-max) does not. (C) 2005 Acoustical Society of America.